Sound Powered Military Headset Microphone Crystal Radio For Sale

Up for
sale is a NOS vintage Chinese Military Balanced Armature Headphone and
microphone. These communications headset microphone were manufactured around
1970, design for the first Chinese Military 15 watt semiconductor transceiver.
This EH-3 headset microphone is a collectable item and will be a welcome
addition to your collection. Perfect for ham transceiver, very good for coping cw signals or crystal radio listening.

Although it is low
impedance (150Ω DC resistance, about 600Ω ~ 1000 Ω impedance), it is extremely
sensitive. As a balanced armature device, it is sensitive enough to be classed
as “sound-powered”, i.e.: if connected to a similar pair of headset, voice
communication is possible without the need for a battery.

If connect this headphone via a
suitable high-low impedance matching transformer (such as a Bogen 7254
watt audio matching transformer or Mouser Electronics 42TM117-RC
50K:1K audio transformer) or directly connected the detector to the appropriate
tap point on the tuning coil, this headphone would be ideally suited for
crystal radio reception. I have tested it in my crystal radio and it sounds
very loud, the sensitivity of this balanced armature headphone is much better
than a good high impedance (DC resistance 2000 or 4000Ω) headphone.

Its microphone has
two 580Ω magnetism elements in series and is installed back to back, this is a
noise cancellation design. When noise goes into both side of the microphone, the
diaphragm will not vibrate too much because the energy from both side are counteract. But
when a operator talk close at one side of the microphone, the diaphragm will vibrate
and produce electric current in the coils.

The microphone sounds
fairly loud as a receiver when connect it to a crystal radio output.

The cable from
headset to microphone is about 2-1/2 foot long, from microphone to the 7 pins
military type connector is about 3-1/2 foot long. The
headphone is connects to pin #3 and pin #5 in the connector with microphone
push button OFF ( the headphone is always on if connects to pin #1 and pin #5
in the connector ). The microphone is connects to pin #2 and pin #4 in the
connector with that push button ON.

The quality of
construction for this headset is great because it was designed for military
application. The balanced armature elements are sealed and very difficult to
open (the inside view pictures of the headphone element were taken from same
type of headset)

Please E-mail any questions you may have before you offer. It is
time to clean up the electronic related items in my garage, please keep an eye
out for my other sales! Thanks for looking!

Please
make payment arrangements within 3 days. I accept PayPal. International payment
must be by PayPal only, in US dollars. Payment is expected within 10 days of
sale closing, or item will be released for sale. International buyer pays
$23.95 shipping charge for US Postal Service Priority Mail.